LTC3216 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
LTC3216
Linear Technology
'LTC3216' PDF : 12 Pages View PDF
LTC3216
BLOCK DIAGRAM
C1+
C1–
C2+
C2–
2
12
1
10
OSCILLATOR
1x MODE: CPO = VIN
1.5x MODE: CPO = 4.6V
2x MODE: CPO = 5.1V
3 CPO
VIN 9
EN2 8
EN1 7
CONTROL
LOGIC
11
GND
VREF
MODE
CONTROL
DROPOUT
DETECTOR
5 ILED
CURRENT
SOURCE
CONTROL
6
4
13
ISET2 ISET1 GND
3216 BD
OPERATION
The LTC3216 uses a fractional switched capacitor charge
pump to power a high current LED with a programmed
regulated current. The part starts up into the 1x mode. In
this mode, VIN is directly connected to CPO. This mode
provides maximum efficiency and minimum noise. The
LTC3216 will remain in this mode until the LED current
source begins to dropout. When dropout is detected,
the LTC3216 will switch to 1.5x mode after a soft-start
period. Any subsequent dropout detected will cause the
part to enter 2x mode. The part may be reset to 1x mode
by bringing the part into shutdown mode and then reen-
abling the part.
A two phase nonoverlapping clock activates the charge
pump switches. In the 2x mode, the flying capacitors are
6
charged on alternate clock phases from VIN. While one
capacitor is being charged from VIN, the other is stacked
on top of VIN and connected to the output. Alternatively, in
the 1.5x mode the flying capacitors are charged in series
during the first clock phase, and stacked in parallel on
top of VIN on the second clock phase. This sequence of
charging and discharging the flying capacitors continues
at a free running frequency of 900kHz (typ).
The current delivered to the LED load is controlled by the
internal programmable current source. Three discrete
current settings (Low, High and Low + High) are avail-
able and may be selected via the EN2 and EN1 pins. The
values of these currents may be selected by choosing
the appropriate programming resistors. Each resistor is
3216fc
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